A balaclava is a hood ... in the shape of a helmet. It covers the entire head and often has an extra piece of fabric at the bottom to be tucked into your jacket.
They are not only comfortable and warm, but also hygienic. Because it is important to keep an eye on things when riding a motorcycle, balaclavas are usually equipped with a number of cut-outs for the eyes or the entire face, depending on what you find comfortable.
The used material can be chosen (partly) according to your own preferences as well. It seems obvious to us that wool is a bad option under a helmet, but plain cotton and even more high-tech materials like microfleece offer what they promise: a healthy and pleasant microclimate inside the helmet.